Cellular networks provide a communications path between each subscriber's mobile phone and a mobile switching center (MSW). The mobile switching center manages communications to and from mobile phones in a variety of locations. These communications travel between the mobile switching center and subscribers' mobile phones through a base station. Typically, several base stations are affiliated with each mobile switching center, and each mobile phone communicates through a base station that is nearby relative to other base stations. As the mobile phone changes location (when, for example, its user is driving in a car), it may also change the base station through which it communicates.
The area in which a mobile phone can communicate with particular base station is known as a cell. Each base station has a radio frequency (RF) antenna, through which it communicates with the mobile telephones within the cell. Each base station also has a backhaul facility, through which it communicates with the mobile switching center to carry mobile telephone conversations within the cell. The backhaul facility typically communicates with the mobile switching center through either a microwave link or a terrestrial wire, such as a T-1 line.
To provide a high quality of mobile phone service, it is desirable for these cells to be adjacent to one another, leaving no intermediate gaps in which cellular phone service is unavailable. Likewise, each cell should be arranged such that its corresponding base station has the capacity to handle all the telephone conversations carried out by users at peak times within the cell. Thus, a central business district in which many mobile telephones are used during the business day is typically provided with a higher density of base stations, each with a smaller cell, than in outlying areas.
Designing a cellular network for a high quality of service involves a number of complicating issues. For example, to avoid gaps in service areas, so-called “coverage holes,” it may appear desirable to design larger cells that are served by base stations with high-power antennas. However, the larger cell would encompass more subscribers and may cause calls to be dropped if the capacity of the base station is exceeded. Another solution—increasing the number (and, accordingly, the density) of base stations—entails a great financial expense, the regulatory and architectural challenge of finding (and leasing) a desirable location for each base station, and the task of arranging for backhaul communications from each new base station to the mobile switching center.
To provide flexibility in the design of mobile telephone networks, remote antenna systems have now become available. A remote antenna system corresponds to a particular base station, but it can be positioned remotely from its corresponding base station. Several remote antennas can be associated with each base station, allowing the cell associated with the base station to extend into carefully controlled areas. For example, if the mobile telephone service provider determines that there is a coverage hole between two existing cells, it can position a remote antenna within that hole and associate that remote antenna with an existing base station.
One available remote antenna system is the Digivance Long-Range Coverage Solution (LRCS), from ADC Telecommunications, Inc., of Minneapolis, Minn. Although remote antenna systems provide additional flexibility to mobile telephone service providers, the service provider must still arrange for communications between the base station and the remote antenna system. These communications typically take place over a fiber optic line. As a result, the service provider must arrange for a terrestrial path between the remote antenna system and the base station. If the remote antenna system is located within the same building (such as a sports arena, for example) as the base station, it may be feasible to run a fiber optic line. This fiber optic tether, however, restricts a more flexible arrangement of base stations and remote antenna system, particularly as the desired separation between the two becomes greater.